The present invention relates to lightweight, flexible, disposable sensors for capturing acoustic sounds, in particular cardiac sounds, and to a method of assembling the sensors.
Acoustic pick-up devices that have been traditionally used for capturing heart sounds have had two distinct disadvantages: (a) they have a poor signal to noise ratio in that they are sensitive to air-borne noise which requires that a special, quiet room be used for procedures involving their use; and (b) they are fairly massive in size and therefore substantially reduce any surface vibrations that they are trying to detect.
Commercially available contact microphones are sometimes used to capture heart sounds because they reduce the pick-up of extraneous sounds. On the negative side however is the fact that they influence the surface vibrations even more than other types of pick-ups.
Many of these devices have an additional disadvantage in that they must be held in place. This can introduce unwanted noise from the unavoidable quivering of muscles and creaking of joints in the user's fingers. Belts could be used to avoid this but many users find them objectionable from a convenience standpoint. Still further, many present sensor devices incur signal losses due to air coupling and non-contaneous conformance with the skin.
Attempts have been made to deal with these problems. In one such attempt, a sensor was developed which employed a biaxially poled polyvinylidene fluoride (PVDF) material, 25 microns thick, coated with aluminum metallization. The aluminum metallization was applied to completely cover both sides and then processed by abrasion to form desired electrode patterns. However, the aluminum had a tendency to react with the conducting transfer adhesive that is used to make internal electrical connections. The reaction by-products caused the electrical contacts to become intermittent so that the sensor failed.